This invention relates to a hydraulic damper of the adjustable damping force type particularly adapted for use in a vehicle such as an automobile.
Various proposals have been made with respect to hydraulic dampers of the adjustable damping force type since it is preferable to change the damping force characteristics of the hydraulic dampers in a suspension system of a vehicle such an an automobile in response to the running condition of the vehicle, such as running on a rough road, running on a paved road at a relatively low speed, running at a high speed and the like, which can improve driving comfort and steering stability.
This invention relates to a hydraulic damper of the adjustable damping force type including a cylinder containing hydraulic liquid therein, a piston working in the cylinder and partitioning the interior thereof into two liquid chambers, a piston rod connected to the piston and extending through one of the liquid chambers to the outside of the cylinder, a coaxial bore formed in the piston rod, a liquid passage for communicating the two liquid chambers and including at least a portion of the bore, an adjusting rod inserted into the coaxial bore and adapted to be operated rotatably from the outside of the damper, and a rotary valve secured to the adjusting rod and having a plurality of circumferentially spaced and radially extending orifices having different diameters for selectively changing the effective passage area of the liquid passage, thereby adjusting the damping force.
One prior art hydraulic damper of the aforementioned kind further comprises a check valve which is resiliently displaceable in the axial direction. The check valve opens, e.g. during the contraction stroke of the damper, to increase the effective passage area and closes during the extension stroke of the damper, thereby reducing the effective passage area.
However, when the check valve is axially displaceably provided the overall axial length of the damper tends to increase and, when the check valve is provided to cooperate with the rotary valve an axial force will act on the rotary valve, particularly when the check valve is in the closed condition thus increasing the force required to operate the check valve. Further, the check valve usually consists of a valve body and a coil spring for biasing the valve body against a valve seat, thus increasing the number of parts and complicating the manufacturing and assembling operation, thereby increasing costs.